Seasonal Changes in the Distribution of Water in the Outer Growth Rings of Fraxinus Mandshurica Var. Japonica: A Study By Cryo-Scanning Electron Microscopy

Abstract

Seasonal changes in the distribution of water in the outer growth rings of Fraxinus mandshurica var.japonica were visualised by cryo-scanning electron microscopy using samples in which water was freeze-fixed in the living trunk . During the growing season from mid-May to late-July when formation ofxylem progressed steadily, all cell lumina of the newly forming xylem elements were filled with water. From August to October, water was lost from the lumina of wood fibres in the current-year xylem. Loss of water from wood fibres began in August at the initial zone of the earlywood, and progressed toward the cambial zone. By November, water had disappeared from the lumina of current-year earlywood vessels, and water reappeared in the lumina of earlywood fibres around the currentyear earlywood vessels. Our results indicate that cavitation in lumina of current-year earlywood vessels occurred during the period from October to November.